Fiber-reinforced load-bearing soft tissues, including tendon, meniscus, and annulus fibrosus, have hierarchical structure and biochemical composition that enables in vivo mechanical function. These tissues are prone to degeneration and injury, with debilitating consequences, high costs, and limited therapeutic options. Although load-bearing tissues are classically described using idealized schematics showing an ordered prevailing fiber direction, these tissues are in fact highly inhomogeneous, with amorphous proteoglycan-rich structural micro-domains within an otherwise ordered collagen-rich fibrous tissue - they are not simply a schematic. The objective of this proposal is to investigate micro-level structure-function of native and engineered tissue by quantifying and modeling mechanics from the tissue to the cellular level, and evaluating the mechanistic impact of micro-level structure-function on mechanotransduction. This study will also recapitulate these natural and/or potentially diseased micro-environments in engineered tissues in order to develop controlled in vitro systems to evaluate altered mechanotransduction. Quantifying the size, mechanical inhomogeneity, and biological response among tissue micro-domains is important because this is the length scale that governs cell mechanotransduction, and therefore regulation of tissue homeostasis and disease progression. These studies will advance the field of regenerative medicine by addressing micromechanical mechanisms in tissue development, degeneration, and injury. Ultimately, this new understanding will direct therapeutic strategies for rehabilitatio, repair, and replacement to promote and preserve healthy mechanotransduction in fibrous load bearing tissues.